1. Field of the Invention
The present invention relates to a compound having the following structure (I): ##STR1## The compound of structure (I) is a trifunctional crosslinking agent which can be added in the presence of other vinyl monomers such as acrylic acid, methacrylic acid, alkyl acrylate, alkyl methacrylate or any other monomer containing a double bonded carbon and then polymerized.
2. Description of the Prior Art
In the past, many attempts have been made to employ carbohydrates for the development of well-characterized novel polymers of some practical significance. The use of sugars and their derivatives in the production of polymers is of growing interest since polymers containing mono- or disaccharides in their main chain or as grafted pendant groups or chains display useful and unique properties such as hydrophilicity, chirality, biological activity, biodegradability, and the like. Furthermore, most sugars are available at economical prices and are industrially produced in large quantities by cultivation in plants and microorganisms, followed by chemical isolation or by degradation of plant waste material followed by isolation. For instance, sucrose is produced on a scale that is larger than any other pure organic chemical, world-wide.
The major problem associated with the use of carbohydrates for developing polymers is the similar reactivity of the primary and secondary hydroxyl groups on the carbohydrate moiety. Hence, when carbohydrates are polymerized non-enzymatically with other monomers, the resulting polymer products are often a mixture of linear, cross-linked and branched chain products. This is due to the reaction of both the primary and secondary hydroxyl groups in the carbohydrate moiety with electrophilic groups in the other monomer.
Many attempts have been made in the past towards polymerizing carbohydrates such as those attempts described by N. Ogata et al. in J. Polym. Sci., Polym. Chem. Ed., Vol. 19, p. 2609 (1981) and Vol. 22, p. 739 (1984); and S. K. Dirlikov, "Monomers and Polymers Based on Mono and Disaccharides", Pacific Polymer Preprints, First Pacific Polymer Conference, December 12-15, 1989, Volume 1, pp. 113-114.
Although Dirlikov, supra, claims that high molecular weight polymers have been made, no proof has been shown that these polymers are strictly linear and do not contain additional cross-linked or branched chain polymers and that only the primary hydroxyl groups react thereby forming a strictly linear polymer.
Sucrose used as a starting carbohydrate for the production of carbohydrate polymers would be ideal since it is produced in vast quantities and is low in price. To synthesize intermediate sucrose derivatives for further use in the production of novel polymers using sucrose as a starting compound is difficult due to the reactivity of the primary hydroxyl groups at carbons 6, 1' and 6' and the remaining five secondary hydroxyl groups.
One such sucrose intermediate is 2,3,3',4,4'-penta-O-methylsucrose having the structure (II) ##STR2##
The compound of structure (II) is useful as an intermediate in the synthesis of other sucrose derivatives that can be used to synthesize various crosslinking agents.
Molecules such as glycerol, sorbitol, 3,5-dihydroxymethylbenzyl alcohol and pentaerythritol are examples of polyfunctional crosslinking agents, in addition to the more commonly used trifunctional crosslinking agent known as 2-ethyl-2-hydroxymethyl-1,3'propanediol or trimethylolpropanetriol. These polyols are traditionally known to crosslink polyesters or may be functionalized further to produce other polyfunctional crosslinking agents. Thus upon treatment of 2-ethyl-2-hydroxymethyl-1,3-propanediol with acryloyl or methacryloyl chloride the well known acrylic and methacrylic crosslinking agents, namely 2-ethyl-2-hydroxymethyl-1,3-propanediol triacrylate and 2-ethyl-2-hydroxymethyl-1,3 -propanediol trimethacrylate are obtained. These crosslinking agents are commonly called trimethylolpropane triacrylate (TMPTA) and trimethylolpropane trimethacrylate (TMPTMA), respectively. Treatment of such an acrylate or methacrylate crosslinking agent with excess methyl acrylate or methyl methacrylate in the presence of a free radical initiator permits polymerization of these molecules to thermoset materials. However, due to the size of trimethylolpropane triacrylate or trimethacrylate and the symmetry of these molecules, only a small separation exists between the reactive ends of the acryloyl or methacryloyl moieties. Hence, some termini cross link the polymerizing methyl acrylate or methyl methacrylate and other termini internally cyclize to create ten-membered rings. In this situation the double bonds of the crosslinking agents are unused.
This internal cyclization or unused double bonds in the crosslinking agent reduces the networking ability of the crosslinking agents. For instance, it is described in Matsumoto et al "Gelation in the copolymerization of methyl methacrylate with trimethylolpropane trimethacrylate," Eur. Polym. J., 25(4), 385-389 (1989) that the crosslinking efficiency of trimethylolpropane trimethacrylate is only 18% and that 82% of the polymer mixture had internally cyclized despite the fact that an excess of methyl methacrylate was present in the polymerizing milieu.
It has been surprisingly discovered that a trimethacryloyl-penta-O-methylsucrose, namely 1',6,6'-trimethacryloyl-2,3,3',4,4'-penta-O-methylsucrose can be prepared from the intermediate of structure (II) via a one step process and that this compound displays little internalization. This compound can be used as a crosslinking agent to strengthen the mechanical properties of various network methyl methacrylate polymers, in addition to polymeric networks created by other vinyl monomers polymerizing by a free radical mechanism.